Accelerometers, acceleration switches, and inertial sensing devices are widely used to measure accelerations (forces resulting from vibrations, changes in velocity, or the like). Such devices may include some sort of sensing mass suspended within the device so as to be affected by acceleration forces so as to move and thereby open or close an electrical contact. The acceleration switch may be filled with damping fluid so as to prevent premature actuation of the switch due to vibration, shocks, or the like.
One possible use for such an acceleration switch is in a rocket arming circuit. For reasons of safety, it may be desired that some circuits aboard the rocket or its payload not be actuated until the rocket has experienced a normal launch environment. For additional safety, it may also be desired that these circuits not be actuated when the rocket or its payload is involved in abnormal environments such as accidental fire or crash during transportation.
In a typical moving mass switch, damping fluid is provided to prevent actuation upon application of a short hi-g force which, typically, would be caused by accidentally dropping the switch onto a hard surface. In addition, if the acceleration of the rocket is sufficient, the moving mass of the switch may be selected such that a launch acceleration over several seconds is sufficient to move the mass through the damping fluid and to overcome the friction of closing switch contacts. However, for certain rockets having a low-g launch profile and limited payload capacity, it has been found that the force associated with the relatively small mass moving through the damping fluid is not sufficient to overcome the friction of closing switch contacts.